Acne is one of the most frequently presented dermatologic conditions. To date there is no single widely accepted treatment modality although a number of approaches exist. These approaches include topical or systemic antibiotics, benzoyl peroxide gels, oral 13-cis-retinoic acid, or hormones. Acne lesions (comedones) are the result of a complex interaction between hormones (androgens) and bacteria (Propionibacterium acnes) in the pilosebaceous unit. Acne results when the opening of the sebaceous glands is occluded, resulting in accumulation of sebum and fatty acids produced by the bacteria through lipase breakdown of lipids. The increase in sebum results in enlargement of the glands which in turn leads to inflammation and eventually to rupture of the glandular envelop. Release of the gland contents into the dermis produces changes in the structural matrix and may result in scarring. While acne is not a life threatening condition, it frequently produces discomfort, and can be disfiguring to a subject due to scarring.
Exposure of the skin to ultraviolet radiation has been reported to result in enlargement of the sebaceous glands. This has been found in photoaging studies in hairless mice. It is also known that sun exposure results in amelioration of acne. The response to sunlight may be either due to photodynamic activity (PDT) of coproporhyrin produced by the bacteria, Propionibacterium acnes, or due to an effect of the sunlight to the cell differentiation and proliferation. The PDT effect would lead to destruction of the bacteria which in turn would lead to improvement of acne. In this case, short wavelength visible radiation (405-410 nm) should be equally effective in improving acne. However, there is substantial evidence that both light and antibiotics reduce the fluorescence produced by coproporphyrin, the loss of which is not always related to amelioration of the acne condition.
The present invention is directed to methods for treating acne. The methods include exposing the subject afflicted with acne to ultraviolet light having a wavelength between about 320 to about 350 nm, such that the acne is treated, e.g., inhibited, diminished, eradicated or prevented. In a preferred embodiment, the wavelength is 335 nm and is emitted by a nitrogen laser, a third harmonic of a NdYAG laser, a tunable OPO laser (Optical Parametric Oscillator), or a properly filtered mercury lamp or continuous wave lamp. Treatments can be administered over a several week period, where the subject is exposed to sequential doses of ultraviolet light to obtain beneficial effects, e.g., a reduction or elimination of the acne, e.g., eradication or diminishment of the bacteria responsible for acne, e.g., Propionibacterium acnes. 
The present invention is also directed to methods for preventing acne. The methods include exposing the subject afflicted with acne to ultraviolet light having a wavelength between about 320 nm to about 350 nm, such that acne is prevented. In one embodiment, ultraviolet wavelengths useful in the invention are between about 325 nm to about 345 nm, preferably between about 330 to about 340 nm, more preferably between about 332 and about 337 nm, and most preferred at 335 nm.
The present invention is also directed to methods for reducing the amount or size of sebaceous glands in a subject. The methods include exposing the subject to ultraviolet light having a wavelength between about 320 and 350 nm, such that the amount or size of sebaceous glands in the subject are reduced.
The present invention is further directed to methods for treating disease states or conditions which cause or are associated with the generation of excess of sebum in sebaceous glands. The invention is also directed to methods for treating disease states or conditions which cause or are associated with the occlusion of sebaceous glands with accumulation of sebum and fatty acids produced by bacteria through lipase breakdown of lipids. These methods include exposing the subject to ultraviolet light having a wavelength between about 320 and 350 nm, such that the buildup of sebum and/or lipids in the sebaceous glands of the pilosebaceous units of the subject are reduced.